1. Field of the Invention
The present invention relates to an apparatus and a method employed to conduct a surface inspection on a test piece such as a wafer during the process of manufacturing IC chips, liquid crystal display panels and the like.
2. Description of Related Art
Many different circuit patterns are stacked over a plurality of layers at a surface of a substrate such as a wafer to manufacture an IC chip or a liquid crystal display element panel. These circuit patterns are formed by stacking them one layer at a time on the wafer through a photolithography process or the like.
When manufacturing an IC chip, for instance, a resist is applied in a thin layer onto an oxide film formed at a surface of a wafer (substrate) and then a circuit pattern at a reticle is exposed onto the resist layer by an exposure apparatus. Next, the resist having been exposed is removed through development processing, thereby forming a pattern constituted of a resist layer achieving an identical form (or a similar reduced form) to the circuit pattern at the reticle. Subsequently, after removing the exposed oxide film through etching, the remaining resist layer is removed to form a circuit pattern constituted of the oxide film layer at the surface of the wafer. An element such as a diode is formed through doping processing or the like implemented on the circuit pattern constituted of the oxide film layer. While there is a degree of variance with regard to the manufacturing method depending upon the type of IC being manufactured, the process of forming a specific circuit pattern layer as described above is normally performed repeatedly to stack a plurality of circuit patterns over many layers on the wafer.
When circuit patterns are stacked over numerous layers on the wafer in this manner, a surface inspection is conducted to verify that no defect, abnormality or the like has occurred in the circuit pattern formed in each layer. This inspection may be implemented when, for instance, a circuit pattern constituted of the resist layer has been formed. If a surface defect, an abnormality or the like such as a deformation of the circuit pattern, inconsistency in the film thickness of the resist layer or a scar is detected during the inspection, reclaim processing is implemented for this circuit pattern layer. Namely, the resist is stripped and then a new resist layer is applied and exposed.
If a defect, an abnormality or the like occurs at any of the circuit patterns when manufacturing an IC chip or the like by stacking the circuit patterns over multiple layers on the wafer, the acceptability of the IC chip as a product is compromised. For this reason, it is crucial to conduct an inspection to detect such defects, abnormalities and the like, i.e., to conduct a wafer surface inspection.
If any defect is detected during the resist development processing stage, reclaim processing can be implemented to eliminate the defect by removing the resist and reapplying the resist layer. However, an area where a defect, an abnormality or the like is detected when a circuit pattern has been formed at an oxide layer or the like through etching cannot be reclaimed. This means that a pattern can be reclaimed by removing the resist pattern layer only as long as surface defects are detected through a surface inspection conducted at the resist development processing stage. Namely, the surface inspection conducted at the resist pattern formation stage is of especially important.
The surface inspections proposed in the related art include an inspection in which various types of inspection illuminating light are irradiated on the test piece (wafer) surface from different angles and the light reflected at the test piece is directly observed visually by the inspector as the test piece is rotated or tilted.
Such an inspection method is generally referred to as a macro inspection. When a macro inspection is implemented through visual observation by the inspector, there is a risk of inconsistency manifesting in the inspection results due to varying judgment criteria, skills and the like among individual inspectors. In addition, the onus placed on the inspector is significant. Accordingly, the possibility of automating macro inspections has been examined and various automatic macro inspection apparatuses have been proposed. For instance, there is an apparatus that performs an automatic surface inspection by irradiating inspection illuminating light onto a surface of a test piece, receiving the diffracted light from a repetitive pattern formed at the surface of the test piece with an image-capturing device to take in a diffracted image and performing image-processing on the diffracted image.
However, in the surface inspection apparatus in the related art, the optimal settings cannot be automatically selected for the apparatus conditions (the illuminating light incident angle, the tilt angle of the test piece substrate, the wavelength of the illuminating light, the position at which the light exiting the test piece and entering the image-capturing device is received and the like) when capturing a diffracted image based upon the diffracted light from the circuit pattern (repetitive pattern) on the surface of the test piece. The optimal settings in this context refer to conditions under which the direction along which the diffracted light originating from the repetitive pattern advances substantially matches the direction along which the optical axis of the light-receiving optical system that receives the diffracted light extends and, in other words, they are conditions under which a diffracted image that is good enough to enable a surface inspection is obtained.
In the surface inspection apparatus in the related art, the diffracted image of the test piece is displayed on the monitor and the inspector selects the optimal settings for the apparatus conditions by checking the diffracted image on the monitor. However, this method poses a problem in that it is not always easy for the inspector to accurately judge the optimal apparatus conditions and the inspector must have significant skills and experience.
In addition, since circuit patterns are formed over numerous layers, as explained earlier, and diffracted light originates from the individual pattern layers, there is a problem in that when a defect is detected based upon a diffracted image, it cannot be ascertained as to the specific layer from which the diffracted image has originated. For instance, a defect occurring during the process of pattern formation at a given layer may be overlooked and may be detected later during a surface inspection conducted after forming a pattern at an upper layer. In such a case, if it is erroneously judged that the defect is present at the uppermost layer, the uppermost resist pattern layer will be removed to reclaim the pattern. However, since the defect is present at the lower layer in reality, the reclaim processing described above will not solve the problem.
Thus, there is a problem with regard to the surface inspection apparatus in the related art in that it cannot be clarified as to whether or not a detected defect is present at the uppermost layer.
An object of the present invention is to provide a surface inspection apparatus and a surface inspection method that make it possible to judge as to whether or not a defect or the like detected in a surface inspection conducted on a test piece having patterns formed over numerous layers is present at the pattern at the uppermost layer.
A surface inspection apparatus according to the present invention is employed to inspect a surface of a test piece having a surface formed by stacking a plurality of pattern layers. This surface inspection apparatus comprises an illuminating optical system that irradiates illuminating light onto the surface of the test piece, an image-capturing device that captures an object image based upon diffracted light from the test piece, a condition control device that sets or changes an apparatus condition at which the object image is to be captured by the image-capturing device and a condition detection device that takes in the object image captured by the image-capturing device every time the apparatus condition is changed by the condition control device and determines an optimal condition for the apparatus condition for inspecting the pattern layers based upon the object image thus taken in. The condition detection device ascertains an optimal condition for the apparatus condition by using an image taken in before forming an uppermost pattern layer, also ascertains an optimal condition for the apparatus condition by using an image taken in after forming the uppermost pattern layer and judges as to whether or not an image captured by the image-capturing device corresponds to the uppermost pattern based upon the plurality of optimal settings thus ascertained.
The condition detection device may either ascertain the optimal condition for the apparatus condition based upon a plurality of images obtained through an image-capturing operation performed at the image-capturing device while changing the apparatus condition or ascertain the optimal condition based upon the relationship of the change in the brightness level detected in a plurality of images corresponding to the change in the apparatus condition. Alternatively, the condition detection device may detect the highest brightness levels corresponding to one of a plurality of images, ascertain the relationship of the change that the highest brightness levels manifest corresponding to the change in the apparatus condition and select as the optimal condition the apparatus condition that corresponds to the peak value among the highest brightness levels obtained by quadratically differentiating the relationship.
The apparatus condition that is changed during the inspection is constituted of at least one of; the angle of incidence at which the illuminating light from the illuminating optical system enters the test piece, the mounting angle at which the test piece is mounted, the wavelength of the illuminating light and the position at which the light exiting the test piece and entering the image-forming device is received.
The surface inspection apparatus may further comprise a defect detection device that detects a defect in a pattern formed at the test piece based upon an image having been captured by the image-capturing device at the optimal condition determined by the condition detection device to correspond to the uppermost pattern. Alternatively, the surface inspection apparatus may further comprise a storage device that stores in memory the image captured by the image-capturing device at the optimal condition determined by the condition detection device to correspond to the uppermost pattern and a defect detection device that reads out the image stored in the storage device and detects a defect at a pattern formed at the test piece based upon the image.
Furthermore, the surface inspection apparatus according to the present invention may include a storage device that stores in memory the optimal condition determined by the condition detection device to correspond to the uppermost pattern to allow the condition control device to read out the optimal condition from the storage device to set the apparatus condition based upon the optimal condition when inspecting a test piece other than the test piece used to determine the optimal condition.
In a surface inspection method according to the present invention, illuminating light is irradiated onto a surface of a test piece having a surface formed by stacking a plurality of pattern layers, an object image is captured based upon diffracted light from the test piece and a surface inspection is conducted based upon the image thus captured. In the surface inspection method, images are taken in by changing an apparatus condition during an image-capturing operation before forming an uppermost pattern layer, an optimal condition for the apparatus condition at which the pattern layer is inspected is ascertained based upon the plurality of images, images are taken in by changing the apparatus condition at which the image-capturing operation is performed after forming the uppermost pattern layer, an optimal condition for the apparatus condition at which the pattern layer is to be inspected is determined based upon the plurality of images and it is judged as to whether or not a captured image corresponds to the uppermost pattern based upon the plurality of optimal settings thus ascertained.
The optimal condition for the apparatus condition may be determined based upon a plurality of images obtained through an image-capturing operation performed by changing the apparatus condition or it may be determined based upon the relationship of the change manifested by the brightness levels detected in a plurality of images corresponding to the change in the apparatus condition. Alternatively, the highest brightness levels each corresponding to one of a plurality of images may be detected, the relationship of the change that the highest brightness levels manifest corresponding to the change in the apparatus condition may be ascertained and the apparatus condition that corresponds to a peak value among the highest brightness levels obtained by quadratically differentiating the relationship may be designated as the optimal setting.
The apparatus condition that is changed is constituted of at least one of; the angle of incidence of the illuminating light, the mounting angle at which the test piece is mounted, the wavelength of the illuminating light and the position at which the light exiting the test piece is received.
A defect at a pattern formed at the test piece may be detected based upon an image having been captured at the optimal condition determined to correspond to the uppermost pattern or may be detected based upon an image captured at the optimal condition determined to correspond to the uppermost pattern stored in memory and then read out.
In the surface inspection method according to the present invention, the optimal condition determined to correspond to the uppermost pattern may be stored in memory and the optimal condition thus stored in memory may be read out to set the apparatus condition based upon the optimal condition when inspecting a test piece other than the test piece used to determine the optimal condition.
In this surface inspection method, it is judged as to whether or not a defect is present at a plurality of pattern layers based upon images that have been captured and the pattern layer at the uppermost position undergoes reclaim processing if a defect is detected at the uppermost pattern layer among the plurality of pattern layers.
A surface inspection apparatus according to the present invention comprises an illuminating optical system that irradiates light on a surface of a test piece having a surface formed by stacking a plurality of pattern layers, a signal output device that detects diffracted light from the test piece and outputs a diffracted light signal corresponding to the quantity of the diffracted light, a condition control device that sets or changes an apparatus condition at which the diffracted light is to be detected by the signal output device and a condition detection device that determines an optimal condition for the apparatus condition at which a pattern layer is inspected based upon the diffracted light signal output by the signal output device when the condition control device changes the apparatus condition. The condition detection device determines an optimal condition for the apparatus condition by using a diffracted light signal output before forming an the uppermost pattern layer, also ascertains an optimal condition for the apparatus condition by using a diffracted light signal output after forming the uppermost pattern layer and judges as to whether or not a diffracted light signal output by the signal output device corresponds to the uppermost pattern based upon the plurality of optimal settings thus ascertained.
In a surface inspection method according to the present invention, light is irradiated by an illuminating optical system onto a surface of a test piece having a surface formed by stacking a plurality of pattern layers, a diffracted light signal corresponding to the light quantity of diffracted light from the test piece detected by a diffracted light detection unit is generated and a surface inspection is performed based upon the diffracted light signal. In this surface inspection method, diffracted light signals from the diffracted light detection unit are taken in by changing the apparatus condition at which the diffracted light detection unit performs detection before forming an uppermost pattern layer, an optimal condition for the apparatus condition at which the pattern layer is to be inspected is determined based upon the diffracted light signals, diffracted light signals from the diffracted light detection unit are taken in by changing the apparatus condition at which the diffracted light detection unit performs detection after forming the uppermost pattern layer, an optimal condition for the apparatus condition is determined based upon the diffracted light signals and it is judged as to whether or not a diffracted light signal provided by the diffracted light detection unit corresponds to the uppermost pattern based upon the plurality of optimal settings thus ascertained.
Alternatively, in a surface inspection method according to the present invention, a test piece having at least two shot areas each formed by laminating a plurality of pattern layers at a surface thereof is illuminated, an object image is captured based upon diffracted light from the test piece and a surface inspection is performed on the test piece based upon the captured object image. In this surface inspection method, a specific pattern layers in the two Or more shot areas are formed through exposure operations performed under varying exposure conditions by an exposure apparatus and other pattern layers in the two or more shot areas are formed through exposure performed under identical exposure conditions at the surface of the test piece, object images of the two or more shot areas are captured by varying the apparatus condition for capturing an object image, changes that the captured images manifest in correspondence to the change in the apparatus condition are ascertained, the changes corresponding to the two or more shot areas are compared and the apparatus condition at which the changes manifest a difference from each other is designated as the optimal condition.
A surface inspection method according to the present invention may be achieved by illuminating a test piece having shot areas each formed by laminating a plurality of pattern layers at a surface thereof, capturing an object image based upon diffracted light from the test piece and performing a surface inspection on the test piece based upon the captured object image. When forming uppermost resist layers through exposure during the shot area formation process in this surface inspection method, the resist layers are formed by varying the exposure condition at which the exposure is performed by an exposure apparatus for at least two shot areas, object images are captured by changing an apparatus condition for each of the two or more shot areas, changes that the images manifest in correspondence to the change in the apparatus condition are ascertained based upon the captured images, the changes corresponding to the two or more shot areas are compared and the apparatus condition at which the changes manifest a difference from each other is designated as an optimal condition at which the uppermost resist layers are inspected. In the surface inspection method, the uppermost resist layers are inspected at the optimal condition to allow a resist layer to be reclaimed if a defect is detected at the resist layer.
When forming the uppermost resist layer through exposure during the shot area formation process a normal pattern is formed at the resist layer in one of the two or more shot areas and a defective pattern is formed at the resist layer at the other shot area. In addition, the test piece is a semiconductor wafer utilized for testing.